This present invention concerns the area of intervertebral arthrodeses (fusion of two vertebrae) and in particular of intersomatic cages implanted between two adjacent vertebrae to allow the insertion and the growth of grafts of osseous tissue (or of substitute) in the disc space. In fact, after the insertion of the cage or implant, the intervertebral space is filled with autologous spongy bone or suitable bone substitutes. The invention also concerns an instrument for implanting the cage between the vertebrae, in particular through the transforaminal approach. The intersomatic cages are designed to be positioned between two vertebrae, in order to restore and/or maintain the disc space by replacing the intervertebral disc, and the grafts of osseous tissue or of substitute are designed to allow fusion between the two adjacent vertebrae between which they are inserted.
Various types of intersomatic cage are known from prior art. Some intersomatic cages known from prior art are machined from bone, most often cortical bone, so as to fuse with the graft inserted into the disc space. These cages composed of bone have the disadvantage to being capable of causing illness in the event of imperfect sterilisation.
Different intersomatic cages in solid materials of various types are also known from prior art. These cages include openings on their lower surface, their upper surface and on at least one of their lateral surfaces. One of these cages, in particular known from patent application WO0187194 (A1) submitted by the present applicant, has the shape of an open ring and can be used in combination with another cage of the same type by placing the open lateral surfaces of the two cages opposite to each other. Whatever the type of cage in question, spongy bone is compacted inside the cage, in order to finally achieve an osseous fusion (or arthrodesis) of the two vertebrae separated by a suitable disc space. Other cages known from previous designs are of parallelepiped shape, with the top and the bottom of the cage being completely open, and the top and bottom openings being designed to be positioned facing two vertebrae which have to be kept apart from each other. Openings created in the lateral faces of the parallelepipeds allow the graft to grow toward the exterior of the cage and possibly to reach a graft implanted in another cage also inserted into the disc space. These intersomatic cages have the disadvantage, firstly, of requiring a relatively large incision in the annulus (the outer part of the intervertebral disc), secondly, of requiring a relatively long time before achieving an arthrodesis, because of the confinement of the graft within a chamber at the centre of the cage and, thirdly, of having dimensions that are too large to be implanted through the transforaminal approach without partial or total ablation of the articular processes located posterior to the foramen through which the transforaminal approach runs.
Also known from previous designs in prior art, in particular from American patent application US 2005/0038511(A1), are intersomatic cages of various shapes and dimensions, machined from bone, and in particular an intersomatic cage of banana (or simple bracket) shape defining a longitudinal axis of the cage and having a lower surface and an upper surface, both straight, equipped with serrations and more or less parallel to the longitudinal axis of the cage, a concave lateral wall, a convex lateral wall, and two straight end walls that are more or less perpendicular to the top and bottom surfaces. One of the end walls of the cage includes a hole oriented toward the centre of the cage and intended to receive a rod of an instrument for insertion of the cage between the vertebrae. This intersomatic cage has the disadvantage of being in osseous tissue and therefore, as mentioned previously, of being capable of causing illness in the event of imperfect sterilisation. This cage may also have the disadvantage of eventually not being sufficiently solid to reliably take the stresses which will be applied to it when implanted in the disc space. Furthermore, this cage has the disadvantage of having a hole oriented toward the centre of the cage and in particular toward the centre of the concave surface, the result of which is to make the cage even more fragile. Moreover, the axis defined by this hole forms an angle, in relation to axis parallel to a tangent to one of the concave and convex surfaces, that is too large to allow to an instrument for insertion of the cage between the vertebrae to fit onto the cage in an orientation that is more or less parallel to a tangent to one of the concave and convex surfaces. Thus, the orientation of the hole does not conform to the general curvature of the cage obtained by its convex and concave surfaces and does not allow an effective thrust to be applied to the cage on its axis of curvature. The cage, which is made fragile by this hole, is therefore in danger of breaking when pressure has to be applied at an angle that is too large in relation to the axis of curvature of the cage, which therefore proves difficult to implant by the transforaminal approach. Finally, withdrawal of the instrument inserted into the hole proves to be difficult due to the unsuitable orientation of the latter.
In this context, it is of interest to propose an intersomatic cage, preferably in a solid and sterile material, that has a shape and dimensions that make it suitable to be implanted through the transforaminal approach without an excessively large lesion of the articular processes, and having resources to fit onto an instrument for insertion of the cage between the vertebrae, with an orientation that conforms to the general shape of the cage. It is also of interest to propose an instrument for implanting the cage, and which is designed for the shapes and dimensions of the cage, allowing easy implantation of the cage between the vertebrae. Also known from prior art are previous designs of instruments for the implantation of intersomatic cages that have at least one rod designed to be inserted into a hole in the cage in order to hold the latter during passage through the foramen. However some of these instruments known from prior art require an ablation of at least one part of the articular processes impeding access to the foramen when the cage and the instrument have excessively large dimensions. Moreover, the transforaminal approach is relatively obstructed and is not perfectly straight. It is therefore desirable that the instrument should have an elbow (a curved or angled portion) at the end holding the cage. Some instruments known from prior art have dimensions that are small enough not to necessitate ablation of the articular processes, and some of these instruments have an angled portion that allows one to bypass the structure obstructing access to the disc space, but the rod designed to hold the cage, as well as the hole of the cage in which this rod is designed to be inserted, have an orientation that it not very compatible with the optimal thrust axis allowing insertion of the cage between the vertebrae and not very compatible with easy withdrawal of the rod when the cage has been implanted. It is therefore desirable to propose an instrument whose shape and dimensions are suitable for insertion using the transforaminal approach, having an angled portion to bypass the structures obstructing access to the disc space and having a rod designed to be inserted into a hole in the cage with an orientation that is optimal in order to facilitate the implantation of the cage between the vertebrae, and then withdrawal of the instrument.